JPH0583601B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a graphite mold for hot pressing for hot pressing powder materials such as ceramics or metals. This invention relates to a graphite mold for hot press that prevents stress concentration and damage during pressurization.

(Prior art) Conventionally, graphite molds for hot pressing have used a graphite die case 1 having a polygonal hole for hot pressing inside and a cylindrical outer shape, as shown in FIG. ing. Such conventional molds have a problem in that stress concentration occurs at the corners of the holes in the die case (points indicated by arrows in FIG. 4) when pressure is applied, making them susceptible to breakage.

In order to prevent this, a conventional method has been to increase the wall thickness of the die case to prevent breakage. Alternatively, a sleeve has been interposed on the inner circumferential surface of the hole in the die case, and the corners of the hole have been curved to prevent stress from concentrating on the corners, thereby preventing damage.

(Problems to be Solved by the Invention) However, when preventing damage by increasing the wall thickness of the die case, the die case becomes large and difficult to handle, increases cost, and has poor thermal efficiency. There's a problem.

On the other hand, when a sleeve is interposed on the inner circumferential surface of the hole in the die case and the corners of the hole are processed into curved surfaces, there is less stress concentration compared to square-shaped ones due to the curved surface, which prevents breakage. Although it is effective, when applying high pressure such as when obtaining a dense sintered body,
As expected, many cracks occur, and a sufficient effect of preventing damage cannot be obtained.

For example, when obtaining a sintered body of silicon nitride, a pressing force of about 500 kg/cm ² is required. For this reason, a number of die cases had to be kept in stock as spares, resulting in a problem of high costs.

The present invention was made in view of the above circumstances, and provides a graphite mold for hot press that prevents stress concentration at the corners of polygonal hot press holes and is highly effective in preventing breakage during pressurization. This is what I am trying to do.

(Means and effects for solving the problems) In order to solve the above problems, the means taken by the present invention is to provide a graphite mold for hot press having polygonal holes for hot press inside. It consists of a die case having a hole and a sleeve that comes into contact with the inner peripheral surface of the hole of the die case, and a circumference that includes the apex of the hole and bulges outward is drawn at the corner of the hole of the die case. The gist of the present invention is a graphite mold for hot pressing, which is characterized by providing an escape space.

In this way, the relief space provided at the corner of the hole in the die case, including the apex of the hole and bulging outward, reduces the stress applied to the corner of the hole when pressurized. It is distributed around the periphery of the relief space and acts to avoid stress concentration at the corners of the hole. Therefore, even when high pressure is applied, such as when obtaining a dense sintered body, a sufficient effect of preventing damage can be obtained.

The graphite mold for hot press according to the present invention is composed of a die case having a polygonal hole and a sleeve that comes into contact with the inner peripheral surface of the hole of the die case. In this case, the sleeve has a polygonal shape of the die case. A structure with a hole divided into each side, or a one-piece structure corresponding to a polygonal hole in a die case are used. With this combination of die case and sleeve, it is possible to fill the filler without being affected by the relief space, and it is economical because only the sleeve needs to be replaced if wear or damage occurs during die cutting. It is also a target.

Note that the hot press method also allows for the sintering of products with complex shapes such as hollow shapes, and pressure forming is sometimes performed by inserting a core as a core into the hot press hole. The graphite mold for hot press according to the above can be applied.

(Example) Examples will be described below with reference to the drawings.

In the embodiment shown in FIG. 1, a square hole for hot pressing is formed in a graphite die case 1 having a cylindrical outer shape, and a divided sleeve 3 is formed on the inner peripheral surface of the hole. are in contact. A circular escape space 2 is formed at the corner of the hole of the die case 1.

In the embodiment shown in FIGS. 2 and 3, the hole for hot pressing in the die case 1 is formed in a rectangular shape, and a divided sleeve 3 is placed on the inner peripheral surface of the hole in the same way as in the embodiment shown in FIG. A circular relief space 2 is formed at the corner of the hole of the die case 1.

Thus, the stress applied to the corner of the hole in the die case 1 during pressurization is dispersed to the periphery of the circular relief space 2, as shown by the arrow in FIG. Due to the effect of dispersing stress in this manner, the shape of the die case 1 can be made to match the shape of the hole for hot pressing, rather than having a cylindrical outer shape as in the conventional case.

(Effects of the Invention) As described above, the graphite mold for hot press according to the present invention includes a die case having a polygonal hole and a sleeve that abuts the inner peripheral surface of the hole of the die case. By providing a relief space at the corner, which includes the apex of the hole and traces the circumference that bulges outward, the stress applied to the corner of the hole when pressurized is dispersed to the periphery of the relief space, and the hole is Damage due to stress concentration at the corners can be prevented.

Furthermore, the wall thickness of the die case can be reduced, saving mold material and improving thermal efficiency when heating during pressurization.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the graphite mold for hot press according to the present invention, FIG. 2 is a cross-sectional view showing another example of the graphite mold for hot press according to the present invention, and FIG. FIG. 4 is a cross-sectional view of a main part of a graphite mold for hot press shown in FIG. 4, and FIG. 4 is a cross-sectional view showing a conventional graphite mold for hot press. Explanation of symbols: 1...Die case, 2...Escape space, 3...Sleeve.

Claims (1)

[Claims] 1 A graphite mold for hot press having a polygonal hole for hot press inside, consisting of a die case having a polygonal hole and a sleeve that comes into contact with the inner circumferential surface of the hole of the die case, A graphite mold for hot pressing, characterized in that a relief space is provided at the corner of the hole so as to trace the circumference that bulges outward and includes the apex of the hole.